can I work out *the* standard deviation from a value given as "+/- 1 standard deviation" I'm confronted by a table of values:
17.1  (16.6)
18.0  (9.5)
38.1 (22.5)
30.6 (16.7)

In the left-hand column we have some mean values. I’m told that the values in parenthesis are 'one standard deviation of the mean'
Which I understand to be a range, within which 68% of values would fall.
What I want to know is THE standard deviation associated with the numbers on the left.
Am I missing something? Is something perhaps wrong with the information supplied to me in the table? If not, is there a way to move from 'one standard deviation'  to 'the standard deviation'. The sample size in every case is 5.
EDIT 
In response to the excellent answers and insights already posted, I have added more detail in the comments. Here is the table I am looking at:


Here is a reference to the information:p184 for the data table in question (Table5), Catena, 2008, 'Surface soil hydraulic properties in four soil series under different land uses and their temporal changes' X. Zhou a,⁎, H.S. Lin a, E.A. White p:184 
 A: To underline the obvious, we don't have any more information than you give, as you don't give a source that we can look at ourselves, or any wider context on what variable or variables are being discussed. Is this something conveyed informally? Can't you illuminate what the context is? Homework? You're the assistant or consultant? 
"one standard deviation of the mean" strikes me as awkward wording. It could mean the standard error of the sample mean. 
From those values, however, my guess is that you are being given the means and in parentheses the standard deviations of various data. So, 17.1 is the mean and 16.6 is the standard deviation of the first set (subset, variable: I am just guessing). 
Note that the 68% you cite is a result for the normal distribution. 68% of the values of a normal distribution lie within 1 SD of the mean. But if your data are not normally distributed, then that may not hold. 
In particular, if your data are for variables that can only be positive, or can only be zero or positive, then the SDs given are roughly the same order as the means, and the implication is that the variables are positively skewed and not normally distributed. If mean $-$ SD is close to zero and negative values are not allowed, then you can't have a normal distribution. 
I have used the words guess and guessing already. Here's a third: this is all just a guess. You don't give enough information for this analysis to be confident. (If someone is garbling or limiting what they tell you, that's not good either.) 
I can't begin to guess what A means. 
My answer is not at all the same as that of @asdf, which should be an extra warning. 
Let me try to end confidently: I can't think that there is a difference in substance between "one standard deviation" and "the standard deviation". 
A: Let us assume that conductivity is non-negative and that there are only two possibilities: standard deviation (sd) and standard error of the mean (sem). Then let us look at the second value for Glenelg which is 1.6 (2.1). Since there are 5 values we know their sum is 1.6 * 5 = 8. The maximum sd for five values adding to 8 of a non-negative variable is found for the values 0, 0, 0, 0, 8 and is 3.58. So the maximum value of the sem would be $3.58 / \sqrt(5 - 1) = 1.79$ which is less than the value of 2.1 quoted. So we deduce that 2.1 cannot be the sem as it is too large so must be the sd.
Note however that this is based on the assumptions stated in the first sentence so we cannot be 100% sure based on the evidence we have.
A: If the numbers in parenthesis are one standard deviation, you can just subtract them from the left "mean" column and get the actual standard deviation, so I think I am not understanding your question.
